Horse Diarrhea: Causes, Emergency Signs & Treatment 

Last updated: December 28, 2025

By: Miles HenryFact Checked

How a Neglected Colt Taught Me to Take Diarrhea Seriously

Winter 2019, a yearling colt at our local livestock auction ran through the ring with no bids. He was BCS 2, rain rot across his back and hindquarters, and watery manure pooling under him in the trailer. When my vet saw him that evening, she didn’t mince words: “Worms. Bad ones. We start aggressive treatment today or you’ll be digging a hole by the weekend.”

We started a vet‑supervised deworming protocol targeting strongyles over several weeks, put him on straight Alicia Bermuda hay (no concentrates until his gut stabilized), and checked his manure twice a day. Within 10 days, his stool changed from liquid to “cow‑plop” consistency. By 8 weeks, he’d gained about 110 pounds and the rain rot had cleared. Today, Jimmy is a solid riding horse.

That colt taught me horse diarrhea is rarely “just diarrhea”—it almost always signals parasites, infection, feed mistakes, or stress. This guide explains the major causes, when you have minutes versus hours to act, and how to prevent diarrhea in the first place.

🚨 60‑Second Diarrhea Triage

Use this when you’re standing in the barn aisle wondering, “Is this an emergency?”

CALL YOUR VET NOW (Emergency)

• Watery or projectile manure (constant stream or large puddles instead of piles)
• Rectal temperature over 101.5°F (normal is about 99–101°F)
• Not drinking or not eating
• Colic signs: pawing, looking at flanks, repeatedly lying down or rolling
• Any foal, any senior (20+), or any horse recently on antibiotics

MONITOR CLOSELY FOR 12–24 HOURS (Then Call if No Improvement)

• “Cow‑plop” consistency (loose but still somewhat formed)
• Normal appetite and drinking
• No fever, bright and interactive

IMMEDIATE ACTIONS FOR ALL CASES

• Isolate the horse from the herd.
• Offer electrolytes in one bucket and plain, clean water in another.
• Take a rectal temperature.
• Do a skin tent test (pinch the skin over the shoulder; it should snap back in under 2 seconds—a method described in this explanation of hydration and skin pinch tests in horses).
• Text or call your vet with what you see, even if you don’t think it’s an emergency yet.

Severe diarrhea can cause life‑threatening dehydration in as little as 6–12 hours, especially in foals and older horses, which mirrors warnings in veterinary discussions of equine colitis and dehydration.

Top 5 Causes of Horse Diarrhea

1. Parasites (Most Common in Neglected or Under‑Managed Horses)

The biggest culprits are strongyles and cyathostomins (small strongyles). Heavy parasite burdens damage the intestinal lining and leak protein and fluid into the gut, as outlined in reviews of equine cyathostomins and their clinical impact.

Typical signs:

• Chronic loose stool
• Weight loss despite eating
• Rough coat, pot belly
• Long hair coat that doesn’t shed normally

Diagnosis: a fecal egg count (FEC). Don’t guess and “just deworm”—your vet can use FEC results to choose the right drug and timing, in line with modern strategic deworming programs for horses.

Why Jimmy improved:

• Vet‑designed deworming that hit different parasite stages over 6–8 weeks
• Clean, consistent forage (Alicia Bermuda hay) rather than rich concentrates while his gut healed

2. Bacterial Infections (Most Dangerous)

Serious bacterial diarrhea is a true emergency. Common causes include:

• Salmonella
• Clostridium difficile or C. perfringens
• Potomac Horse Fever (Neorickettsia risticii)

These can cause:

• Sudden onset of profuse, watery manure
• Fever, depression, and refusal to eat
• Rapid dehydration and risk of endotoxemia, which can trigger laminitis

The Merck Veterinary Manual’s section on salmonellosis in horses details how quickly these horses can deteriorate and why aggressive IV fluids, anti‑inflammatories, and sometimes plasma are needed.

Risk factors:

• Recent stress (travel, weaning, competition)
• Recent antibiotic use (kills “good” gut bacteria)
• Contaminated feed or water
• Recent colic episode

These infections are often contagious, and some (like Salmonella) can affect humans, as discussed in Salmonella infection summaries for horse owners. Isolate affected horses and follow your vet’s instructions carefully.

3. Sand Enteropathy (Sandy Regions)

In Louisiana and other sandy areas, horses can ingest significant sand while grazing short pasture or eating off bare ground. Sand accumulates in the colon, irritates the lining, and can cause both diarrhea and colic, a condition described in detail in the Merck entry on sand enteropathy in horses.

Signs:

• Chronic loose stool, often with gritty feel
• Intermittent, mild colic
• Weight loss despite adequate feed

Simple “sand test” at home (with your vet’s guidance):

• Place fresh manure in a clear glove or bag
• Add water, mash gently, and hang it so contents settle
• After several minutes, look for a layer of sand at the bottom

Diagnosis (veterinary):

• Sand sedimentation tests and rectal exam
• Abdominal radiographs if needed

Treatment may include:

• Psyllium for several days (dose and duration per your vet; a recent clinical study on medical treatment of sand accumulation with psyllium and magnesium sulfate supports this approach)
• Magnesium sulfate or other medications via nasogastric tube under vet supervision

Prevention:

• Avoid feeding directly on sand
• Prevent overgrazing to “golf‑course height”
• Use periodic psyllium under your vet’s guidance for horses on sandy soils

4. Diet & Feed Changes

Feed mistakes are a very common cause of loose manure and are highlighted in many owner‑level diarrhea guides, such as this Mad Barn overview of diarrhea causes in horses.

Common triggers:

• Switching hay or grain abruptly instead of over 7–10 days
• Turning out on lush spring grass for hours at a time from day one
• Feeding large, starchy grain meals
• Using moldy or poor‑quality hay

Sudden changes disrupt the hindgut microbiome. Fiber‑digesting bacteria die off, harmful species can bloom, and fermentation patterns shift—resulting in diarrhea.

Prevention:

• Use a 10‑day transition when changing hay or grain (gradually increase the new feed, decrease the old).
• Never change hay and grain at the same time—change one, then the other.
• Introduce spring pasture slowly, starting with short turnout and increasing as long as manure stays normal.
• Base the diet on quality grass hay (Alicia Bermuda, Timothy, Orchardgrass), similar to recommendations in general equine nutrition requirements.

5. Antibiotics & Pain Medications (NSAIDs)

Antibiotic‑associated diarrhea (AAD) happens when antibiotics wipe out beneficial gut bacteria, allowing harmful bacteria (including Clostridium species) to overgrow. Equine referral practices have documented AAD in hospitalized horses, as reviewed in studies of antimicrobial‑associated diarrhea in equines.

Non‑steroidal anti‑inflammatories like phenylbutazone (Bute) and flunixin (Banamine) can also damage the gut lining when overused or given at incorrect doses.

Prevention:

• Never use leftover antibiotics or drugs borrowed from another horse; antibiotics must be prescribed by your vet for this horse’s specific problem.
• Consider a vet‑recommended probiotic during and shortly after antibiotic courses. A review by Kentucky Equine Research outlines current evidence in their article on probiotics for horses with diarrhea and hindgut issues.
• Follow your vet’s dosing and duration for Banamine and other NSAIDs exactly—don’t increase or extend treatments on your own.
• Monitor manure daily while a horse is on antibiotics or high‑dose NSAIDs.

Special Note: Foals

Foal diarrhea should always be treated as urgent because foals dehydrate much faster than adults. Owner resources like SmartPak’s guide to diarrhea in horses and foals note that “foal heat diarrhea” around 7–14 days old is usually mild and self‑limiting, but it can look similar to more serious conditions.

Common foal‑related causes:

• “Foal heat” diarrhea at 7–14 days
• Rotavirus and other viral infections
• Cryptosporidium and other protozoa
• Lawsonia intracellularis (proliferative enteropathy)
• Rhodococcus equi (often with concurrent pneumonia)

Even if you suspect foal‑heat diarrhea, call your vet—it is far better to be told it’s normal than to miss an early warning sign of something serious.

🚨 When to Call the Vet Immediately

Use this as your barn’s “do not wait” checklist. On the site, render this as a styled box rather than showing the code.

• Watery or projectile manure: constant stream or puddles instead of piles
• Fever: rectal temperature above 101.5°F
• Colic signs: pawing, looking at flanks, lying down repeatedly, obvious discomfort
• Dehydration: skin tent stays raised for more than 3 seconds
• Gum changes: pale, dark red, or tacky gums; capillary refill time over 3 seconds
• Laminitis red flags: heat in hooves, reluctance to walk, shifting weight from foot to foot
• High‑risk horses: any foal, horses over 20, or horses that have had antibiotics in the last 2 weeks
• Duration: any diarrhea lasting more than 24 hours, even if the horse still seems bright

Severe diarrhea and colitis are repeatedly flagged in veterinary manuals as emergencies because endotoxemia and dehydration can progress rapidly to shock and laminitis, as discussed in the Merck Veterinary Manual’s sections on colitis in adult horses.

How Vets Diagnose Diarrhea

At‑Home Checks (Before or While You Call)

You can do these safely while waiting for your vet:

Check	How to Do It	What It Tells You
Skin tent	Pinch neck/shoulder skin, release	Stays up >2 seconds = dehydration
Gum color & CRT	Press gums, time color return	>2–3 seconds = poor circulation
Temperature	Use rectal thermometer	>101.5°F = likely infection
Manure volume	Note whether piles vs puddles	Flooding = more urgent
Eating/drinking	Watch 15–30 minutes	Not eating or drinking = serious

This explanation of CRT and skin pinch tests in horses shows how vets use the same basic checks.

Common Veterinary Tests

Your vet chooses tests based on severity, age, and risk factors:

• Fecal tests
  • Fecal egg count (parasites)
  • Flotation and sedimentation (parasites and sand)
  • Cultures or toxin assays for Salmonella, Clostridium, etc.—many labs bundle these into standardized “equine diarrhea panels,” such as those described by IDEXX Equine Reference Laboratories
• Blood work
  • Complete blood count (CBC): infection, inflammation
  • Serum chemistry: kidney, liver, electrolytes
  • Fibrinogen and other inflammatory markers
• Advanced diagnostics
  • Fecal PCR panels that check multiple pathogens at once, as offered by several vet schools’ equine diarrhea PCR panels
  • Abdominal ultrasound to assess gut wall thickness and motility
  • Rectal exam to check for impaction or displacement

In severe cases, your vet will also check digital pulses and hoof temperature because endotoxemia from severe diarrhea can lead to laminitis.

Following these tips can help prevent your horse from getting diarrhea.

Treatment: What to Expect

Treatment depends on cause and severity, but the goals are the same: protect life, restore hydration, and address the underlying problem.

Emergency Cases

These are the watery, febrile, dehydrated horses that meet the “STOP & CALL” criteria.

Your vet may recommend:

• IV fluids and electrolytes to replace losses and support circulation—standard practice in severe colitis, as outlined in emergency care articles on treating diarrhoea cases in horses.
• Medications which can include:
  • Anti‑inflammatories that help with pain and the effects of endotoxins
  • Appropriate antibiotics if a bacterial cause is confirmed or strongly suspected
  • Plasma transfusions in some severe Salmonella or colitis cases to help bind toxins and support the immune system
• Supportive care
  • Stall rest with good footing and deep bedding
  • Close monitoring of temperature, heart rate, manure output, and hydration

Most true emergency diarrhea cases are safest in a hospital setting for at least a few days.

Mild / Uncomplicated Cases

For loose stool without fever or systemic illness, with your vet’s approval:

• Hydration support
  • Fresh water at all times
  • Electrolytes offered in a separate bucket
• Diet:
  • Free‑choice grass hay (Alicia Bermuda, Timothy, Orchardgrass)
  • No grain or rich concentrates until the manure has been normal for several days
  • No lush pasture during an active bout
• Probiotics / gut support:
  • Vet‑recommended probiotics can support hindgut recovery after stress or antibiotic use. Current evidence on probiotic use in horses is summarized in reviews such as this open‑access paper on clinical efficacy of probiotics and the KER overview mentioned earlier.
  • Psyllium may be used if sand is suspected, under your vet’s guidance.

If mild diarrhea doesn’t start to improve within 24 hours, or if new signs (fever, colic, not drinking) develop, treat it as an emergency.

Chronic Diarrhea

Chronic cases (lasting weeks) require a thorough workup first. Management may include:

• Low‑starch, high‑forage diet
• Small, frequent meals (3–4 times daily)
• Gradual, one‑change‑at‑a‑time feed adjustments
• Parasite control, sand management, and treatment for any underlying disease (for example, inflammatory bowel disease as described under intestinal disorders other than colic).

Avoid over‑the‑counter anti‑diarrheal medications unless your vet specifically recommends them—slowing gut motility can trap toxins.

Prevention Strategies That Actually Work

1. Strategic, Fecal‑Based Deworming

Modern parasite control focuses on FEC‑based programs rather than fixed‑interval rotation, in line with guidelines summarized in resources like AAEP Internal Parasite Control Guidelines.

Basic framework (to review with your vet):

• Spring and fall fecal egg counts on all horses
• Deworm only high shedders (for example, over 200 eggs per gram) as advised by your vet
• Low shedders may only need 1–2 treatments per year
• Product choices and timing should follow your vet’s advice and local resistance patterns

You can note which products you and your vet typically use in your region, but keep it clear this is an example, not a universal prescription.

2. Pasture & Manure Management

Good pasture management lowers parasite and sand risk:

• Pick manure regularly in small paddocks and dry lots.
• Drag and rest larger pastures during warm, dry weather.
• Rotate grazing to avoid overgrazing down to bare soil.
• In sandy areas, avoid feeding directly on the ground.

3. Feed Management: The 10‑Day Change Rule

To protect the hindgut microbiome:

• Any change in hay, grain, or pasture access should take about 10 days.
• Never switch hay and grain at the same time—change one, then the other.
• Introduce spring grass slowly, starting with short turnout and increasing as long as manure stays normal.
• Use soft, clean grass hay (such as Alicia Bermuda in your area) as the base of the diet, consistent with general equine nutrition recommendations.

4. Stress Reduction and Biosecurity

Stress and exposure drive many diarrhea cases:

• Keep feeding and turnout schedules as consistent as possible.
• For travel and competition, consider vet‑approved gut support and always offer hay and familiar‑tasting water.
• Isolate new arrivals for 2 weeks with their own buckets and tools, just as biosecurity guides for infectious diarrhea in adult horses recommend.
• During any diarrhea outbreak, isolate affected horses, disinfect equipment, and protect people with gloves and good hygiene, especially if Salmonella is suspected.

📋 My Barn Diarrhea Prevention Protocol (30 Years Refined)

This is what works in my barn, always with my vet involved. Use it as a template to discuss your own program with your veterinarian.

Deworming

• Spring and fall: fecal egg counts on every horse.
• Deworm only horses above your vet’s threshold for high shedding, using drug choices based on FEC results and regional resistance patterns.
• A yearly “clean‑up” treatment for encysted strongyles/tapeworms when your vet recommends it.

Feed Management

• Base forage: soft, palatable grass hay (Alicia Bermuda at my place).
• 10‑day minimum for any feed change.
• Never change hay and grain at the same time.
• Limit spring grass initially, then increase slowly if manure stays normal.

Emergency Kit

• Electrolyte powder
• Digital thermometer + lubricant
• Vet‑prescribed Banamine with written dosing instructions
• A probiotic product my vet is comfortable with
• My vet’s cell number saved in my phone
• Gloves and a clean bag or glove to collect a fecal sample

Daily Monitoring

• Check manure consistency at least once a day.
• Note appetite, water intake, and any behavior changes.
• If anything is “off,” I take temperature and check hydration first.

FAQs About Horse Diarrhea

Final Thoughts: Treat the Cause, Not Just the Symptom

Jimmy’s case was never really “about” diarrhea—it was about a heavy parasite load, poor management, and a gut that needed time and support to heal. The diarrhea was the loudest warning sign.

Across three decades, most serious diarrhea cases have fit into a few buckets: parasites, feed changes, stress, and infections in already stressed horses, which matches the patterns described in veterinary summaries of diarrhea causes and complications in horses. Owners who do best are the ones who:

• Call their vet early.
• Follow treatment plans exactly.
• Monitor manure, temperature, and hydration like they matter—because they do.
• Fix the root cause instead of just hoping the diarrhea goes away.

If you’ve managed a tough diarrhea case, sharing what worked (and what didn’t) can help the next owner catch it earlier and act faster.